In mineral ore flotation, depression comprises steps taken to prevent the flotation of a particular mineral. In one mineral flotation systems, it is commonly practiced to hold down both the gangue materials and low-assay middlings. In differential flotation systems, it is used to hold back one or more of the materials normally floatable by a given collector.
Depression is conventionally accomplished through the use of reagents known as depressing agents, or more commonly, depressants. When added to the flotation systems, the depressing agents exert a specific action upon the material to be depressed thereby preventing that material from floating. The exact mode of this action remains open to speculation. Various theories have been put forth to explain this action; some of which include: that the depressants react chemically with the mineral surface to produce insoluble protective films of a wettable nature which fail to react with collectors; that the depressants, by various physical-chemical mechanisms, such as surface adsorption, mass-action effects, complex formation, or the like, prevent the formation of the collector film; that the depressants act as solvents for an activating film naturally associated with the mineral; that the depressants act as solvents for the collecting film; and the like. These theories appear closely related and the correct theory may ultimately prove to involve elements from several, if not all, of them.
Sylvinite ores contain various amounts of KCl (sylvite) and NaCl (halite). Besides sylvite and halite, sylvinite ores also contain small amounts of water insoluble clay, which forms a slime that interferes with the separation of KCl from the ore. Flotation processes are widely used to beneficiate KCl from the sylvinite ores by flotating the KCl from the NaCl. The ground ore is suspended in a saturated solution of the soluble constituents, which also contains insoluble clay. The addition of amine collector and frother to the ore slurry gives a froth containing predominantly KCl. However, in the presence of clay, the amine collector tends to be adsorbed by the clay particles and decreases the efficiency of the separation process. By using the depressant of this invention, a substantial improvement in KCl recovery was accomplished. While not wishing to be bound by any theory, it is believed that the depressant may hinder the adsorption of the amine collector on the clay particles by blocking or "blinding" them. If this is true, the entire amount of added collector may then be utilized for KCl recovery, resulting in the observed increased KCl recovery.
Currently, sylvinite ore flotation processes have utilized depressants derived from natural substances such as starches, dextrins, guar gums, carboxymethyl cellulose and the like. See U.S. Pat. No. 3,456,790 to Fash, U.S. Pat. No. 3,371,778 to Iwasaki, D.P. No. 919,703 and U.S. Pat. No. 2,364,520. However, from an ecological vantage point, the presence of residual depressants such as these in the waste waters may increase the biodegradable oxygen demand and the chemical oxygen demand, which, if of sufficient magnitude, might create a potential for pollution problem in the disposal of these waste waters. From a commercial vantage point, there are an ever-increasing number of countries in which use of reagents having a food value, such as starch, is prohibited in commercial applications. Furthermore, the starch-type depressants require a complex preparation of the reagent solution involving a cooking stage prior to solution and the resultant reagent is susceptible to bacterial decomposition thereby requiring storage monitoring.
Accordingly, there exists the need for a synthetic depressant which can at once overcome the drawbacks of the conventional depressants currently utilized and yet perform in an equivalent or superior manner.
Various depressants, also referred to as blinding agents, used in these flotation systems have been described in U.S. Pat. No. 3,452,867 to Bishop; U.S. Pat. No. 3,782,546 to Kirwin; U.S. Pat. No. 3,805,951 to Brogoitti; U.S. Pat. Nos. 2,288,497 and 2,364,520; and in German Offen No. 1,267,631 to Budan and Canadian Pat. No. 932,485 to Fee. Various other nonsulfide mineral ore depressants have been described in U.S. Pat. No. 3,572,504 to DeCuyper; U.S. Pat. No. 2,740,522 to Aimone and U.S. Pat. No. 3,929,629 to Griffith as well as in U.S.S.R. Pat. Nos. 130,428 to Gurvich and 141,826 to Livhits.
In all of the aforementioned references, the depressants disclosed are distinct in structure and properties than those employed in the instant process.
In our U.S. Pat. No. 4,289,613, the ultimate parent of this application, we disclose the use of synthetic depressant in the flotation of iron oxide and SiO.sub.2. The froth consists mainly of SiO.sub.2 (non value) whereas the underflow contains mostly iron oxide (value). In Example 22 of aforementioned patent we illustrated the nature of depressive action of synthetic depressant in the separation of sylvite from halite/clay. In contrast to the iron oxide/SiO.sub.2 flotation, the froth consists here mostly of sylvite (value) while the underflow contains mainly halite/clay (non value); however, as was indicated in the example, the degree of separation was of the order of magnitude experienced in the iron oxide SiO.sub.2 separation.